1. Field of the Invention
The present invention relates to a paper-feeding roller and a method of manufacturing the paper-feeding roller. More particularly, the present invention relates to a paper-feeding roller having a high degree of flexibility and moldability and having improved performance of feeding objects such as paper for plain paper copy (PPC) and capable of effectively preventing non-feeding of silica paper.
2. Description of the Related Art
The rubber roller is used in a paper-feeding mechanism of an ink jet printer, a laser printer, an electrostatic copying apparatus, a facsimile apparatus, an automatic teller machine machine (ATM), and the like. The rubber roller is required to feed objects such as a sheet of paper or a film by picking up the objects one by one separately from the objects piled up one upon another. Therefore, the rubber roller is demanded to have a high degree of flexibility and wear resistance.
The paper-feeding roller of this kind is desired to feed various kinds of printing media such as paper for PPC, silica paper, Chinese paper, an OHP film, and photo-printing paper by picking them up one by one separately without non-feeding thereof.
As disclosed in Japanese Patent Application Laid-Open No. 11-236465, the present applicant proposed the paper-feeding roller composed of the thermoplastic elastomer composition formed by mixing the rubber component, the hydrogenated styrene thermoplastic elastomer, and the olefin resin with one another; dynamically crosslinking the rubber component with the resinous crosslinking agent; and dispersing the rubber component in the hydrogenated styrene thermoplastic elastomer and the olefin resin. In the thermoplastic elastomer composition, the mixing ratio of the hydrogenated styrene thermoplastic elastomer as well as the olefin resin to the rubber is set to a certain range. Thereby the paper-feeding roller composed of the thermoplastic elastomer composition is favorable in its wear resistance, friction coefficient, compression set, and capable of preventing occurrence of blooming. Thus the paper-feeding roller is superior in its feeding performance.
The paper-feeding roller disclosed in Japanese Patent Application Laid-Open No. 2-70636 has the rubber layer containing 100-300 parts by weight of the softener and 10-300 parts by weight of titanium oxide for 100 parts by weight of EPDM (ethylene-propylene-diene rubber) in the surface thereof. The paper-feeding roller is intended to prevent ultraviolet rays from deteriorating its friction coefficient by the use of the EPDM rubber and the titanium oxide.
The paper-feeding roller disclosed in Japanese Patent Application Laid-Open No.2001-38971 is composed of silicone rubber containing the inorganic fibrous reinforcing material and the inorganic particulate filler. Titanium oxide is exemplified as the inorganic particulate filler. The proposal is intended to provide the paper-feeding roller superior in unadhesiveness to tack paper which has adhesiveness on the back side of thermal recording paper.
However, the paper-feeding roller proposed by the present applicant and disclosed in Japanese Patent Application Laid-Open No. 11-236465 has a possibility of non-feeding of paper containing much silica, in the case where it feeds a large number of the paper containing much silica, although the paper-feeding roller has a high friction coefficient for plain paper. Thus the paper-feeding roller has room for improvement in the feeding force for the silica paper or the like.
The vulcanized EPDM rubber roller and the vulcanized chlorinated polyethylene rubber roller hitherto used are liable to give rise to non-feeding for silica paper. Further these substances have a low moldability.
Since the paper-feeding roller disclosed in Japanese Patent Application Laid-Open No. 2-70636 contains the EPDM rubber only, the paper-feeding roller has a low force for feeding paper Immediately after the paper is started to be supplied to the roller and has problems that the material has a low moldability and the manufacturing cost is high.
Since the paper-feeding roller disclosed in Japanese Patent Application Laid-Open No.2001-38971 is composed of the silicone rubber, the paper-feeding roller has a low force for feeding paper immediately after the paper is started to be supplied to the roller. Further the cost of the material for the paper-feeding roller is high and has a low moldability.
The present invention has been made in view of the above-described problems. Therefore it is an object of the present invention to provide a paper-feeding roller having rubber-like durability, elasticity, flexibility, resin-like moldability, and a high wear resistance and a sufficient force for feeding silica paper.
To solve the above-described problem, the present invention provides a paper-feeding roller formed by cylindrically molding a thermoplastic elastomer composition containing a thermoplastic resin or a thermoplastic elastomer in which a rubber or a thermoplastic elastomer which can be crosslinked is dispersed by dynamic crosslinking. A surface layer of the paper-feeding roller contains titanium oxide at not less than 1.5% nor more than 50% in a volume fraction.
The thermoplastic elastomer composition of the paper-feeding roller of the present invention contains the thermoplastic resin or the thermoplastic elastomer in which the rubber or the thermoplastic elastomer which can be crosslinked is dispersed by dynamic crosslinking. Therefore the paper-feeding roller has a rubber-like durability, elasticity, flexibility, resin-like moldability, and a high wear resistance. The paper-feeding roller contains the titanium oxide at not less than 1.5% nor more than 50% in a volume fraction in its surface layer which contacts objects such as paper. Therefore the paper-feeding roller reduces the degree of non-feeding of silica paper which is a problem to be solved and has a preferable feeding force before and after paper is supplied thereto.
The amount of the titanium oxide to be contained in the surface layer of the paper-feeding roller in a volume fraction is not less than 1.5% nor more than 50%, favorably not less than 3.0% nor more than 45%, and more favorably not less than 6.0% nor more than 40%.
If the amount of the titanium oxide is contained in the surface layer of the roller in the volume fraction at less than 1.5%, it is impossible to obtain sufficient feeding force for silica paper. If the amount of the titanium oxide is contained in the surface layer of the roller in the volume fraction at more than 50%, the roller has a high hardness. Consequently the roller has a low friction coefficient or a low mechanical strength. Thus there is a possibility that the roller cannot be put into practical use.
The surface layer means the range of the thickness of the roller less than 5% and preferably less than 3% of the entire thickness thereof from the upper surface thereof. The surface layer may appear when the wear of the roller advances during the use thereof. In the case of a dynamically crosslinked material, a skin rich in resin and not crosslinked thermoplastic elastomer is formed on the surface layer of the roller. Thus it is necessary that the amount of the titanium oxide contained in the resinous phase (matrix phase) falls in the above-described range.
It is preferable that the thermoplastic elastomer composition is formed by dispersing a compound (B) containing a rubber component whose main component is EPDM by dynamic crosslinking in a compound (A) containing a styrene thermoplastic elastomer as a main component thereof. Thereby it is possible to increase an initial friction coefficient of the roller for plain paper and also increase the feeding force thereof for initial and subsequent feeding of silica paper. Thus the roller is capable of displaying high and stable feeding force for various kinds of paper.
The compound (A) contains not less than 15 nor more than 500 parts by weight of a softener and favorably not less than 25 nor more than 400 parts by weight of the softener for 100 parts by weight of the rubber component. Thereby the roller is allowed to have an appropriate degree of flexibility and elasticity.
If the compound (A) contains less than 15 parts by weight of the softener for 100 parts by weight of the rubber component, the roller has a high hardness and thus it is difficult to provide the roller with a sufficient feeding force. On the other hand, if the compound (A) contains more than 500 parts by weight of the softener for 100 parts by weight of the rubber component, the softener may bleed from the surface of the dynamically crosslinked substance or the softener may inhibit crosslinking. Thus the rubber component is not crosslinked sufficiently, and the property of the dynamically crosslinked substance is liable to deteriorate.
The compound (A) contains not less than 1 nor more than 50 parts by weight of a resin whose main component is an olefin resin, favorably not less than 2 nor more than 40 parts by weight of the resin, and more favorably not less than 4 nor more than 35 parts by weight of the resin for 100 parts by weight of the rubber component. Thereby the wear resistance of the roller can be improved.
If the compound (A) contains less than 1 part by weight of the resin, it is difficult for the roller to obtain a sufficient degree of wear resistance. If the compound (A) contains more than 50 parts by weight of the resin, the roller has a high hardness and thus it is difficult to provide the roller with a sufficient feeding force.
The compound (B) contains not less than 15 nor more than 600 parts by weight of a softener and favorably not less than 25 nor more than 400 parts by weight of the softener for 100 parts by weight of the rubber component. Thereby the roller is allowed to have a proper degree of flexibility and elasticity.
If the compound (B) contains less than 15 parts by weight of the softener for 100 parts by weight of the rubber component, the roller has a high hardness and thus it is difficult to provide the roller with a sufficient degree of feeding force. On the other hand, if the compound (B) contains more than 600 parts by weight of the softener for 100 parts by weight of the rubber component, the softener may bleed from the surface of the dynamically crosslinked substance or the softener may inhibit crosslinking. Thus the rubber component is not crosslinked sufficiently, and the property of the dynamically crosslinked substance is liable to deteriorate.
Supposing that the rubber is oil-unextended type, 100 parts by weight of the rubber component means 100 parts by weight of the oil-unextended type. Supposing that the rubber is oil-extended type, 100 parts by weight of the rubber component means the weight of only the rubber component obtained by subtracting the weight of the oil component from that of the oil-extended rubber. If the rubber is a mixture of the oil-extended rubber and the oil-unextended rubber, 100 parts by weight of the rubber component means the weight of the total of the weight of the rubber component obtained by subtracting the weight of the oil component from that of the oil-extended rubber and the weight of the oil-unextended rubber.
As the softener, oil and plasticizer can be used. As the oil, it is possible to use known synthetic oil such as paraffin oil, naphthenic oil, mineral oil of aromatic series, oligomer of hydrocarbon series, and process oil. As the synthetic oil, it is possible to use oligomer of xcex1-olefin, oligomer of butane, and amorphous oligomer of ethylene and xcex1-olefin. As the plasticizer, it is possible to use dioctyl phthalate (DOP), dibutyl phthalate (DBP), dioctyl sebacate (DOS), and dioctyl adipate (DOA).
In the compound (B) containing the rubber component whose main component is the EPDM, it is most favorable that the rubber component consists of the EPDM only. In blending the EPDM and other rubbers, the ratio of the EPDM to all the rubbers is favorably not less than 50 wt % and more favorably not less than 80 wt %. The paper-feeding roller to be used for office appliances is required to be ozone-resistant and heat-resistant. Thus to allow the paper-feeding roller to be ozone-resistant and heat-resistant, it is preferable to set the ratio of the EPDM to the above-described range. The reason is as follows: The EPDM consists of saturated hydrocarbon and does not contain double bond in the main chain. Thus even though the EPDM is exposed to a high-concentration ozone atmosphere or environment which is radiated with light beams for a long time, the main chain of the EPDM is hardly cut and hence ozone-resistant and heat-resistant.
In addition to the EPDM, diene rubbers can be preferably contained in the rubber compound (B) as rubber components or rubbers which can be crosslinked. As the diene rubbers, it is possible to use chloroprene rubber (CR), natural rubber (NR), butadiene rubber (BR), styrene butadiene rubber (SBR), isoprene rubber (IR), and acrylonitrile-butadiene rubber (NBR). These rubbers are used singly or in combination. In the case where the diene rubber is used in combination with thermoplastic resin, it is possible to use a crosslinking agent which crosslinks the diene rubber but does not crosslink the thermoplastic resin. In addition, it is possible to use butyl rubber, ethylene propylene rubber, acrylic rubber, and chlorosulfonated polyethylene rubber.
In the case where the above-described rubbers are used as the oil-extended rubber, it is preferable that the above-described rubbers have a possible largest molecular weight to prevent bleeding of the oil, reduce the compression set of the composition, and improve the wear resistance of the roller. In the case of using EPDM as the rubber, it is possible to use Esprene 670F produced by Sumitomo Chemical Co., Ltd., Esprene 601F produced by Sumitomo Chemical Co., Ltd., and KELTAN 509xc3x97100 produced by DMS Copolymer, Inc.
As the olefin resin, olefin resins commercially available can be used: polyethylene, polypropylene, ethylene ethyl acrylate resin, ethylene vinyl acetate resin, ethylene methacrylate resin, ionomer resin, polyester resin, and chlorinated polyethylene. These resins can be used singly or in combination of two or more thereof. Other thermoplastic resins may be used.
As the styrene thermoplastic elastomer, it is preferable to use a mixture of a high-molecular-weight styrene thermoplastic elastomer having a number-average molecular weight not less than 80,000, favorably not less than 150,000, and more favorably not less than 250,000 and a low-molecular-weight styrene thermoplastic elastomer having a number-average molecular weight not more than 70,000 and favorably not more than 60,000. Thereby it is possible to improve the mechanical property of the composition containing the high-molecular-weight resin, improve the durability of the roller during supply of paper thereto, suppression of generation of worn powder, allow very favorable dispersibility of the rubber, considerably improve processability, and thereby considerably increase the amount of the rubber. The increase of the rubber leads to drastic reduction of worn powder and improvement of durability of the roller. In addition to the (poly)styrene thermoplastic elastomer, it is possible to use other thermoplastic elastomers such as the polyolefin thermoplastic elastomer, the polyester thermoplastic elastomer, the polyamide thermoplastic elastomer, and polyurethane thermoplastic elastomer.
The number-average molecular weight of the high-molecular-weight styrene thermoplastic elastomer is set to nor more than 80,000 to allow the thermoplastic elastomer composition to have preferable mechanical property (wear resistance and durability). The number-average molecular weight of the low-molecular-weight thermoplastic elastomer is set to not more than 70,000 to improve the moldability and processability of the thermoplastic elastomer composition and improve the dispersibility of the rubber. In the case where both the high-molecular-weight styrene thermoplastic elastomer and the low-molecular-weight styrene thermoplastic elastomer are used, those skilled in the art can select a preferable combination. For example, it is preferable to select a combination of a styrene-ethylene-ethylene/propylene-styrene copolymer (SEEPS) having a molecular weight of not less than 80,000 and a styrene-ethylene-ethylene/propylene-styrene copolymer (SEEPS) or a styrene-ethylene/propylene-styrene copolymer (SEPS) having a molecular weight of not more than 70,000. In addition, it is possible to appropriately select a combination from among a styrene-ethylene-styrene copolymer (SES), SEPS, SEEPS, and a styrene-ethylene/butylene-styrene copolymer (SEBS).
As the styrene thermoplastic elastomers having different number-average molecular weights, a hydrogenated styrene thermoplastic elastomer is preferable. The double bond of the hydrogenated styrene thermoplastic elastomer is saturated with hydrogenation and has a low hardness and a high friction coefficient. Thus the hydrogenated styrene thermoplastic elastomer does not have a reaction with a crosslinking agent and thus is not crosslinked therewith in the dynamic crosslinking of the rubber. Therefore, the hydrogenated styrene thermoplastic elastomer does not inhibit the crosslinking of the rubber, and the dynamically crosslinked thermoplastic elastomer composition displays its required plasticity. Accordingly, it is preferable to use the styrene thermoplastic elastomer which is hydrogenated in such an extent that it is not crosslinked in the dynamic crosslinking of the rubber. By addition of a non-hydrogenated elastomer (SBS, SIS, and the like) within limits not damaging processability, it is possible to increase the mechanical strength of the roller by crosslinking between the resin and the rubber. As the hydrogenated styrene thermoplastic elastomer, it is possible to use the styrene-ethylene-styrene copolymer (SES), the styrene-ethylene-ethylene/propylene-styrene copolymer (SEPS), the styrene-ethylene-ethylene/propylene-styrene copolymer (SEEPS), and the styrene-ethylene/butylene-styrene copolymer (SEBS).
The weight ratio between the high-molecular-weight styrene thermoplastic elastomer and the low-molecular-weight styrene thermoplastic elastomer is 95:5-1:99 and favorably 90:10-5:95, and more favorably 75:25-15:85.
If the weight ratio is out of range of 95:5-1:99, there is a possibility that the rubber roller has deteriorated mechanical strength and that worn powder is generated. An optimum weight ratio therebetween can be selected appropriately according to the purpose of use and the relationship between the styrene thermoplastic elastomer and other components.
A resinous crosslinking agent can be used preferably to perform the dynamic crosslinking. The resinous crosslinking agent is a synthetic resin used to allow the rubber to make a crosslinking reaction by heating or the like. Unlike the case in which sulfur and a vulcanizing accelerator are used, the use of the resinous crosslinking agent makes it difficult for blooming to occur and makes the compression set of the thermoplastic elastomer composition low. Therefore the resinous crosslinking agent is preferable because it is superior in keeping accuracy and durability of the roller. Phenol resin can be preferably used to enhance the paper-feeding performance of the roller.
As other resinous crosslinking agents, melamine-formaldehyde resin, triazine.formaldehyde condensate, hexametoxymethyl-melamine resin can be used. Phenol resin is most favorable. As the phenol resin, it is possible to use phenol resins synthesized by reaction of phenols such as phenol, alkylphenol, cresol, xylenol, and resorcin with aldehydes such as formaldehyde, acetic aldehyde, and furfural. It is preferable to use alkylphenol-formaldehyde resin resulting from reaction of formaldehyde and alkylphenol having alkyl group connected to the ortho position or the para position of benzene, because the alkylphenol-formaldehyde resin is compatible with rubber and reactive, thus making a crosslinking reaction start time comparatively early. Alkyl group of the alkylphenol-formaldehyde resin has 1-10 carbon atoms. Thus methyl group, ethyl group, propyl group and butyl group are exemplified. It is possible to use modified alkylphenol resin formed by addition condensation of para-tertiary butyl phenol sulfide and aldehydes; and alkylphenol sulfide resin as the resinous crosslinking agent. The resinous crosslinking agent is used at favorably not less than 1 part by weight nor more than 50 parts by weight and more favorably not less than 8 parts by weight nor more than 15 parts by weight for 100 parts by weight of the rubber component.
The dynamic crosslinking in the present invention may be accomplished in the presence of halogen (chloride, bromide, fluoride, and iodine). To allow the halogen to be present in the dynamic crosslinking reaction, a halogenated resinous crosslinking agent is used or a halogen donor is added to the elastomer composition. As the halogenated resinous crosslinking agent, halogenated resins of addition condensation type can be used. Above all, halogenated phenol resin having at least one halogen atom connected to the aldehyde unit of the phenol resin is favorable. Halogenated alkylphenol formaldehyde resin is most favorable because it is compatible with rubber and reactive and makes a crosslinking reaction start time comparatively early.
As the halogen donor, tin chloride such as stannic chloride, ferric oxide, and cupric chloride can be used. Chlorinated polyethylene can be used as the halogenated resin. The halogen donors can be used singly or in combination of two or more thereof.
A crosslinking activator may be used to accomplish the cross-linking reaction properly. Metal oxide is used as the crosslinking activator. As the metal oxide, zinc oxide and zinc carbonate are preferable.
In addition to the resinous crosslinking agent, it is preferable to use peroxides in performing the dynamic crosslinking reaction because the use of the peroxides makes it difficult for blooming to occur and decreases the extent of the compression set. The dynamic crosslinking reaction may be performed by using sulfur.
In the case where the peroxide is used to perform the dynamic crosslinking reaction, the following peroxides can be selectively used as necessary: 2,5-dimethyl-2,5-di(t-butyl peroxy)hexyne-3; 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane; and dicumyl peroxide. In performing the crosslinking reaction by using the peroxide, to improve and adjust the mechanical properties of the roller such as fatigue characteristic and improve crosslinking density, the following crosslinking co-agents may be used: triallyl isocyanurate (TAIC), triallyl cyanurate (TAC), trimethylolpropane methacrylate (TMPT), and ethylene glycol dimethacrylate (EDMA). As necessary, resin and sulfur be used in performing the crosslinking reaction by using the peroxide.
A filler may be contained in the thermoplastic elastomer composition as necessary to improve its mechanical strength of the roller. As the filler, it is possible to use powder such as silica, carbon black, clay, talc, and the like. It is preferable that the thermoplastic elastomer composition contains not more than 60 parts by weight of the filler for 100 parts by weight of rubber. If the filler is used at more than 60 parts by weight, the flexibility of rubber may deteriorate.
The thermoplastic elastomer composition may contain an age resistor, wax, and the like. As the age resistor, it is possible to use imidazoles such as 2-mercaptobenzimidazole; amines such as phenyl-xcex1-naphthylamine, N,Nxe2x80x2-di-6-naphthyl-p-phenylenediamine, and N-phenyl-Nxe2x80x2-isopropyl-p-phenylenediamine; and phenols such as di-t-butyl-p-cresol, and styrenated phenol.
The hardness of the rubber roller of the present invention is 15-50 and favorably 20-45 when its hardness is measured by an A-type hardness tester of JIS6301. The paper-feeding roller having the hardness in this range deforms sufficiently when it is pressed against paper or a film at a comparatively small force. Consequently the paper-feeding roller contacts the paper or the film in a large area.
The paper-feeding roller cylindrically formed has a thickness of 0.5 mm-20 mm and preferably 1 mm-15 mm. If the paper-feeding roller has a very small thickness, it is difficult to form a large area of contact between the rubber roller and paper when the rubber roller deforms, although the strength of the paper-feeding roller should be considered. On the other hand, if the paper-feeding roller has a very large thickness, it is necessary to press the paper-feeding roller against the paper at a great force to deform the rubber roller. In this case, it is necessary to enlarge the mechanism for pressing the rubber roller against the paper.
The present invention provides a method of manufacturing the paper-feeding roller, which comprising the steps of dispersing a rubber or a thermoplastic elastomer which can be crosslinked in a thermoplastic resin or a thermoplastic elastomer by dynamic crosslinking by using an extruder or a kneader; kneading a composition obtained by performing the dynamic crosslinking again by the extruder or the kneader; adding titanium oxide to the composition to obtain a thermoplastic elastomer composition; and molding the thermoplastic elastomer composition cylindrically.
As described above, after the rubber or the thermoplastic elastomer which can be crosslinked is dispersed by dynamic crosslinking in the thermoplastic resin or the thermoplastic elastomer by using an extruder or a kneader, titanium oxide is added to the composition. Thereby the titanium oxide is allowed to be located in the surface layer of the paper-feeding roller. Therefore it is possible to efficiently improve the volume fraction of the titanium oxide present in the surface layer of the paper-feeding roller and dispose the titanium oxide in the neighborhood of the surface of the paper-feeding roller which feeds paper in contact therewith. Accordingly it is possible to prevent an unnecessary use of the titanium oxide and save the cost of the material for the paper-feeding roller.
Normally, much resin is present in the surface layer of the paper-feeding roller formed by the extruder or the injection molding machine. The titanium oxide has a characteristic that it hardly enters a dynamically crosslinked rubber phase and is selectively mixed with the resin or uncrosslinked thermoplastic elastomer. Thus in the manufacturing method of the present invention, the titanium oxide is selectively disposed in the resin of the thermoplastic elastomer, namely, in the surface of the paper-feeding roller.
It is preferable that the heating temperature in the dynamic crosslinking reaction is 160xc2x0 C.-200xc2x0 C. and that the heating time period is 1-20 minutes. It is preferable that the heating temperature when the titanium oxide is added to the thermoplastic elastomer composition is 160xc2x0 C.-220xc2x0 C. and that the heating time period is 1-20 minutes. It is preferable to swell the thermoplastic resin or the thermoplastic elastomer in a softener in forming the compound (A) containing the styrene thermoplastic elastomer at its main component. Preferably, the composition obtained by the dynamic crosslinking is pellet like. Thereby it is possible to obtain a preferable moldability.
As the extruder, a biaxial extruder can be used. As the kneader, an open roll, a Banbury mixer, and inclosed-type kneader can be used. The paper-feeding roller of the present invention can be produced by a conventional method instead of the manufacturing method of the present invention. It is possible to accomplish the dynamic crosslinking reaction with the titanium oxide contained in the thermoplastic elastomer composition.